Effect of water content on the flowability of hygroscopic powders

Hygroscopic powders adsorb water from air humidity, increasing their cohesion and decreasing their flowability. Maltodextrin, pectin and starch powders were used to evaluate the correlation between flow factor and water content expressed both, as absolute moisture, and as water activity. Powder water content was adjusted through exposition to high relative humidity atmospheres. Maltodextrin and starch powders did not change their flowing behavior within the studied range, remaining easy-flow and cohesive powders respectively. Pectin powder, on the other hand, adsorbed water up to 12% (w/w), modifying its flowability from free-flow, to easy-flow, to cohesive powder. Powders flow factor changed as water content increased in all tested conditions. However, flow factor showed to be better correlated to water activity than to absolute moisture content. These results suggest water activity may be a better parameter to describe the effect of water content on powder flowability than absolute moisture.